Neil Gorsuch testifies before the Senate Judiciary Committee on his nomination to be an associate justice of the US Supreme Court during a hearing in the Hart Senate Office Building in Washington, DC on March 22, 2017.

WASHINGTON — Senate Democratic opposition to President Donald Trump’s Supreme Court nominee swelled Friday as Democrats neared the numbers needed for a filibuster, setting up a showdown with Republicans who have the votes to confirm Neil Gorsuch.

Sens. Claire McCaskill of Missouri, Richard Blumenthal of Connecticut and Brian Schatz of Hawaii became the latest Democratic senators to announce their opposition to Gorsuch, a 49-year-old federal appeals court judge in Denver whose conservative rulings make him an intellectual heir to the justice he would replace, the late Antonin Scalia.

McCaskill’s decision came a day after she said she was torn over the decision. She said she’s opposing the federal appeals court judge because his opinions favor corporations over workers and he’s shown “a stunning lack of humanity” in some of those decisions.

She also criticized Trump in her statement announcing her opposition, saying “the president who promised working people he would lift them up has nominated a judge who can’t even see them.”

Senate Minority Leader Chuck Schumer of New York warned Republicans against changing Senate rules, which could prove momentous for the chamber and would allow all future Supreme Court nominees to get on the court regardless of opposition from the minority party. He says President Donald Trump should just pick a new nominee if Gorsuch is blocked.

Blumenthal, a Senate Judiciary Committee member who questioned Gorsuch on judicial independence and other topics in last week’s hearings, complained that the judge didn’t give straightforward responses.

“We must assume that Judge Gorsuch has passed the Trump litmus test — a pro-life, pro-gun, conservative judge,” Blumenthal said in a statement.

There are now at least 36 Senate Democrats who oppose Gorsuch and have pledged to block him with a filibuster, just five shy of the number that would be required to mount a successful filibuster. All of the Senate’s 52 Republicans are expected to support him. The vote is expected next week.

Republicans are furious at the Democrats’ plans, arguing that filibusters of Supreme Court justices have been exceedingly rare, and accusing Democrats of responding to political pressures from a liberal base that still hasn’t accepted Trump’s election win. Senate Majority Leader Mitch McConnell, R-Ky., is expected to respond to a Democratic filibuster by unilaterally changing Senate rules to lower the threshold for Supreme Court justices from 60 votes to a simple majority in the 100-member Senate.

Although such a change might seem procedural or obscure, it is known on Capitol Hill as the “nuclear option” because it would amount to a dramatic departure from Senate norms of bipartisanship and collegiality.

Changing Senate rules would not be unprecedented. In 2013, Democrats were in the majority and upset about appellate court nominees getting blocked. They pushed through a rules change lowering the vote threshold on all nominees except for the Supreme Court from 60 to a simple majority.

Schumer warned against the rules change in an interview with The Associated Press on Thursday, arguing that Republicans would be the ones to blame if it does occur.

“Senate Republicans are acting like if Gorsuch doesn’t get 60 votes they have no choice but to change the rules,” Schumer said. “That is bunk.”

Schumer’s comments came after Sens. Joe Manchin of West Virginia and Heidi Heitkamp of North Dakota became the first two Democrats to announce their support for Gorsuch, and the only ones so far. Manchin said in a statement, “I hold no illusions that I will agree with every decision Judge Gorsuch may issue in the future, but I have not found any reasons why this jurist should not be a Supreme Court Justice.”

Manchin and Heitkamp are both up for re-election next year in states that Trump won in the presidential election, as is McCaskill. In her statement, McCaskill said she wasn’t comfortable with either decision.

“I remain very worried about our polarized politics and what the future will bring, since I’m certain we will have a Senate rule change that will usher in more extreme judges in the future,” she said.

If confirmed, Gorsuch would replace Scalia, who died in February 2016. But if one of the more liberal justices dies or retires, Trump’s next pick could fundamentally alter the balance of the court. Justice Ruth Bader Ginsburg is 84 and fellow liberal Justice Stephen Breyer is 78. Justice Anthony Kennedy, the pivotal vote closest to the court’s center, is 80.

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